Cancer is now believed to result from unlimited growth of a given cell, which is often due to a block in the ability of cells to undergo differentiation and/or apoptosis. Most of our understanding of how cells grow and divide comes from the study of cells grown in vitro. The cell cycle is typically divided into four phases, G1, S, G2 and M. The periods associated with DNA synthesis (S phase) and mitosis (M phase) are separated by gaps called G1 and G2 (Malumbres, M.; Barbacid, M. Nat. Rev. Cancer 2001, 1, 222-231; Sherr, C. J.; McCormick, F. Cancer Cell 2002, 2, 103-112; Grana, X,; Reddy, E. P. Oncogene 1995, 11, 211-219). The last two decades have seen a series of discoveries, which have provided us with a better understanding of the complexity of the control mechanisms, which ensure ordered progression of cell cycle. It is becoming apparent that the order and timing of the cell cycle is critical for accurate transmission of genetic information, and consequently a number of biochemical pathways have evolved to ensure that initiation of a particular cell cycle event is dependent on the accurate completion of the others. These biochemical pathways have been termed ‘Checkpoints.’
Most normal cells, unless they have received a stimulus to proliferate or differentiate, remain in a resting state, termed Go. However, when the organism requires additional cells, extracellular stimuli induce the cells to enter the G1 phase of the cell cycle and become committed to cell division. It is at a late point in the G1 phase of the cell cycle that a potentially dividing cell reaches the “restriction point,” a time at which the cell must determine whether the conditions are suitable for continued proliferation (Blagosklonny, M. V.; Pardee, A. B. Cell Cycle 2002, 1, 103-105; Donjerkovic, D.; Scott, D. W. Cell Res. 2000, 10, 1-16; O'Connor, P. M. Cancer Surv. 1997, 29, 151-182). Provided that conditions are conducive to proliferation, the cell proceeds past this checkpoint. An absolute prerequisite for cell growth is the duplication of its genetic material, which occurs during the S phase. Once the DNA has been replicated, the cell “ascertains” whether this process has been correctly executed during the second checkpoint during G2, and provided that it has, the cell divides during mitosis, or M phase (Millard, S. S.; Kof, A. J. Cell Biochem. 1998, suppl. 30-31, 37-42). The ordered growth process seen in normal cells is a result of regulatory control mechanisms that restrain cell cycle machinery. The genetic changes seen in a malignant cell are primarily aimed at overriding this negative regulation and result in the loss of one or both of the intrinsic checkpoints that are normally used by their normal counterparts. While some of the oncogenes, such as ras, force progression through G1, other genes such as Rb, which are termed tumor suppressor genes, function as “gatekeepers” of these restriction points (Mc Donald, E. R.; El-Diery, W. S. Ann. Med. 2001, 33, 113-122; Ewen, M. E. Prog. Cell Cycle Res. 2000, 4, 1-17). Cancer is characterized by a loss of one or more tumor suppressor genes, which enables a malignant cell to ignore all of the safeguards that are aimed at preventing unwanted cell division.
An important rule associated with cell cycle progression (for both normal and tumor cells) is the fact that once a cell crosses the “restriction point” (which is the G1/S boundary), it has to either divide into two daughter cells or die4 due to the fact that most eukaryotic cells can exist in S, G2 and M phases of the cell cycle for only a limited span of time. Most chemotherapeutic agents, such as paclitaxel, that are currently used in cancer therapy function by blocking cell cycle progression at a point beyond G1/S boundary (M phase in the case of paclitaxel), resulting in the death of the tumor cell (Wang, T.; Wang, H.; Soong, Y. 88, 2619-2628). A major problem with many of the current drugs is their inability to discriminate between normal and tumor cells. As a result, normal cells undergoing active cell division also become blocked at the mitotic phase of the cell cycle and enter programmed cell death pathways, the effects of which are often manifested as the toxic side-effects seen in patients treated by these drugs. A second problem appears to be the development of resistance to many of the chemotherapeutic agents often due to over-expression of drug transporters. Our quest was to design new chemical entities that exhibit reduced toxicity in normal cells and are not recognized by drug transporters that are over-expressed in drug-resistant tumor cells.
What are needed are methods of preparing effective antiproliferative, radioprotective and chemoprotective activity agents. The methods and compositions of the present invention satisfy these and other long felt needs with the following invention that provides the synthesis of a group of styryl benzyl sulfones which induce apoptotic death of a wide variety of human tumor cell lines at sub nanomolar concentrations while exhibiting relatively low toxicity to normal human cells. More importantly, compounds prepared by these methods were found to be active against a wide variety of human tumor cell lines that are resistant to the activity of many of the cytotoxic agents.